Gel electrophoresis is a technique used to separate and analyze samples, such as DNA, RNA, and proteins, based on their size and/or electrical charge. Sample molecules, such as DNA, can be moved through a gel under the influence of an electric field. Samples can be loaded into a gel and placed inside an electrophoresis chamber, which can be connected to a power source to generate an electric field.
A molecule's rate of migration through the gel can depend on several factors, including the length, conformation, and charge of the molecule as well as the type and porosity of the gel. Nucleic acids are commonly separated in agarose gels. In this situation, shorter molecules can move faster, and therefore migrate farther over a given time, through the pores of the gel. This process is called sieving. In other situations, for example the separation of proteins in agarose, the gel pores may be too large to sieve the molecules. Proteins are commonly separated in polyacrylamide gels, either in their native state or after denaturing. The electrophoretic mobility of a native protein can depend on the length, charge, and conformation of the protein. The electrophoretic mobility of a denatured protein can depend on its length and its mass-to-charge ratio. In some cases, proteins can be denatured using sodium dodecyl sulfate (SDS), which linearizes and negatively charges proteins. This results in an even distribution of charge per mass, which can result in a separation approximately by size alone.